This invention relates to the distillation of fatty alcohols of 6-20 carbon atoms.
Fatty Alcohols can be produced from fatty acids in two different ways: by esterifying the acids to the methyl esters and subsequent hydrogenation to the alcohols, or by direct hydrogenation (Chem. Eng. 2/21/83, page 42). When two phases are formed, the aqueous phase is decanted off from the alcohol phase, and water dissolved in the alcohol phase is separated by distillation. The distillate comprises not only water but also volatile substances, such as hydrocarbons, esters, and the like, as well as methanol.
Esterification and simultaneous continuous separation of thus-formed water and of excess methanol can be conducted in a reaction column as well. Water can also be removed by azeotropic distillation with butanol (French Pat. No. 1,493,754 corresponding to British Pat. No. 1,173,217).
In a process for processing C.sub.1 to C.sub.8 alcohols prepared from synthesis gas (Russian Pat. No. 480,693) as well as hydrocarbons, the aqueous, homogeneous phase in a first step after hydrogenation, is freed of C.sub.1 to C.sub.5 alcohols and water by joint evaporation thereof.
Another process describes the separation of water and hydrocarbons in three distillation columns (CA 88 [1978]: 52282 e).
All of these processes have the common disadvantage that the distillation procedure to separate water is expensive.
Since the fatty alcohols are thermally unstable at temperatures above 250.degree. C., the distillation must be conducted under a column pressure (at its head) of about 400 mbar or less. This requires both vacuum apparatus and the use of refrigeration. Furthermore, with relatively large proportions of dissolved water, i.e., equal to at least 5% by weight, the distillation is made considerably more difficult due to delays in boiling. The water separated by distillation contains--even after additional separation of methanol by distillation--volatile organic components. Therefore, before the water can be passed to waste, another chemical treatment is required. One process, for example, describes the cumbersome route of esterification, hydrogenation, amination, and rectification of the esters. Purification of the higher alcohols (for example the oxo synthesis) for the purpose of eliminating acids, esters, colorants, and the like, takes place by means of pure sodium and alkali washing (French Pat. No. 1,493,743 corresponding to British Pat. No. 1,173,217 and French Pat. No. 1,464,954 corresponding to U.S. Pat. No. 3,359,335).
Separation of the alcohols into the various desired fractions is accomplished by rectification.
Accordingly, the working-up operations used in the prior art are very cost-inefficient.